Calcium Flashcards
How does pH affect the amount of ionised calcium in the body?
Increased pH results in increased albumin binding, and thus less ionised calcium
visa versa, acidosis leads to elevated ionised calcium
40% of plasma calcium is bound to albumin
How does PTH affect calcium levels?
Low calcium, low vit D or high phopshate stimulate PTH production by parathyroid glands
Gut absorption
Renal reabsorption (in addition to phosphate reabsorption)
Bone reabsorption
How is vitamin D obtained by the body?
Vitamin D endogenously synthesised in the skin, forming D3, cholecalciferol
Vitamin D2 is exogenously found in the diet (fish, milk, liver) as ergocalciferol. It’s hydroxylated twice, liver then kidneys.
Causes of vit. D deficiency
diet
lack of sunlight
malabsorption
liver kidney disease
What is calcitonin?
Calcitonin is a hormone secreted by parafollicular cells of the thyroid in response to elevated calcium
It reduces calcium levels by antagonising PTH
Removal of the thyroid, and complete calcitonin deficiency does not lead to overt hypercalcaemia.
Extreme hypersecretion of calcitonin by tumours rarely produces hypocalcaemia.
It is likely that PTH / Vitamin D levels are adjusted in response to calcitonin changes.
What factors determine the intestinal uptake of calcium?
The amount of ionised calcium in the lumen
The amount of activated vitamin D
Factors determining renal excretion of calcium?
90% of renal excretion of calcium is related to sodium reabsorption in the proximal tubule, with 10% regulated by PTH in the distal tubule.
Symptoms of hypercalcaemia
Bones: pain of bones, pathological fractures, muscle weakness
Stones: renal stones, AKI/CKD
Abdominal groans: abdo pain, vomit, constipation, pancreatitis, GI ulcers
Psychic moans: depression, confusion, hypotonicity, tiredness
Investigations for primary parathyroidism?
ECG: reduced QT interval
Bloods:
PTH raised, calcium raised, reduced phosphate
ALP raised
24h urinary calcium: raised. Important to rule out familial hypocalciuric hypercalcaemia.
• Can present similarly.
• Can use a spot calcium:creatinine excretion alternatively. DXA scan: vital to assess extent of osteoporosis.
o Hand XRs show classic subperiosteal bone resorption.
Tumour localization;
o Technetium scanning: show areas of increased uptake. o USS: requires highly skilled operator.
How do you differentiate primary from tertiary?
Normally clinical presentation, but phosphate levels elucidating
What endocrine syndromes are associated with primary hyperparathyroidism?
MEN 1
Parathyroid hyperplasia/ adenoma.
Pancreatic endocrine tumours: gastrinoma / insulinoma. Pituitary adenoma.
MEN 2a;
Thyroid: Medullary carcinoma. Adrenal: PCC.
Parathyroid: hyperplasia.
MEN 2b
MEN 2a + mucosa! neuromas + marfanoid appearance. No hyperPTH.
Describe the investigation and early clinical management of a patient presenting with acute hypercalcaemia.
If Ca2+ >3.Smmol/L and severe symptoms; IV fluids.
o 0.9% NaCl to increase calcium clearance.
o Aim for 3-GL over the first 24 hours.
o Diuretics no longer routinely used, but may be considered if there is a
risk of overload. Bisphosphonates.
o Single dose of pamidronate.
o Lowers calcium over 2-3 days. Calcitonin.
o May be used to rapidly reduce levels in life-threatening hypercalcaemia, however effects are short lived.
Dialysis.
o May be required if there is renal impairment.
Further management is related to investigating and treating the cause of the hypercalcaemia.
Steroids can be useful in hypercalcaemia due to myeloma, lymphoma or sarcoid.
Symptoms of hypocalcaemia
Peripheral Irritability;
o Tetany / cramps.
o Carpo-pedal spasm.
• Wrist flexion and fingers drawn together.
• Happens especially after occlusion of the brachiaI artery, e.g.
with a blood pressure cuff: Trosseau’s sign.
• Tapping over the facial nerve causes twitches: Chvostek’s sign.
Central irritability; o Seizures.
Depression/ anxiety. Perioral paraesthesia. Cataracts.
Ivx hypocalcaemia
Serrum calcium : low.
Serum PTH: high/ low.
o Check parathyroid antibodies if low.
Serum vitamin D: to look for deficiency. ECG: prolonged QT.
Treat hypocalcaemia
Mild/Moderate symptoms; o AdCal: Calcium and vitamin D. Severe symptoms; o Calcium gluconate IV, 10mls of 10% bolus then maintenance infusion. o Start AdCal without delay.
